The invention generally relates to acousto-optic beam deflectors (AOBD) and acousto-optic modulator (AOM) devices, and relates in particular to control systems for such devices.
Acousto-optic beam deflector devices and acousto-optic modulator devices are well-known in the field of laser processing systems and are useful for high-speed beam positioning. U.S. Patent Application Publication No. 2008/0164240 discloses systems and methods for multi-pulse laser processing that includes an AOM device that is driven by a radio frequency (RF) drive signal that is amplitude modulated to provide impingement and non-impingement intervals to respectively transmit or block laser pulses. U.S. Patent Application Publication No. 2009/0095722 discloses systems and methods for laser processing (cutting) links in a memory device in memory repair applications wherein one or more AOBD is configured to deflect the processing laser beam.
Acousto-optic beam devices however, can be temperature sensitive. With passive cooling, RF power applied at constant rate may maintain constant device temperature, but RF power used to deflect beams in certain laser processing application is intermittent.
U.S. Pat. Nos. 5,712,722 and 5,742,425 disclose the use of a modulator that receives multiple RF carrier signals, and produces a constant RF power signal to an AOM. These patents disclose that by choosing the compensating power level, the spatial thermal energy distribution inside the AOM may remain substantially constant.
U.S. Pat. No. 6,295,157 discloses the use of two different RF signals for simultaneously driving an AOM. The power level of each one RF signal is adjusted for pattern writing, and the sum of the load power of both RF signals is disclosed to be maintained substantially constant.
U.S. Pat. No. 6,765,709 discloses the use of electro-thermal strips that are disclosed to provide thermal compensation for transient thermal effects in the bulk material of an optical modulator system. The electro-thermal strips, however, are disclosed to introduce a desired thermal energy to the bulk material to maintain a constant thermal condition.
U.S. Pat. No. 7,616,669 discloses controlling the thermal loading of an AOM by providing RF pulses to the AOM at a constant repetition rate. The RF pulses, however, include RF pulses that are timed to be in coincidence with a laser output, and non-coincident pulses that are not coincident with the laser output. The non-coincident pulses are disclosed to be delayed (e.g., by 0.5 microseconds) such that each occurs immediately after a laser output pulse. The non-coincident pulses are also disclosed to have RF power values and RF durations that are either the same or different than those of the coincident pulses.
There remains a need, therefore, for improved thermal loading methods and systems for maintaining constant or substantially constant AOM and AOBD device temperature.